A process of preparing cellulose fiber using NMMO as a solvent is widely used to produce articles made of cellulose such as film or fiber because the process is pollution-free process by recycling all the used solvent and the article such as film or fiber manufactured by the process has high mechanical strength. The process is disclosed in the U.S. Pat. No. 3,447,935 and so on.
U.S. Pat. Nos. 4,142,913, 4,144,080, 4,196,282 and 4,246,221 disclose a process for making a fiber in which cellulose is swollen in NMMO aqueous solution which contains less than 50% water, and then, the water in the resultant NMMO aqueous solution is distilled under reduced pressure so as to make crude spinning solution, followed by extruding into the fiber.
These processes, however, requires relatively long time so that the physical, chemical properties of the fiber made by the processes are deteriorated due to thermal-decomposition.
And these processes also requires relatively large amount of energy so that the cost of production is too high.
PCT WO 1994/06530 discloses a process for making cellulose solution by removing water using a thin-layer distilling apparatus. This process, however, has some disadvantages, in that an apparatus for implementing the process is too complicated and the production efficient is too low to make viscose cellulose solution.
U.S. Pat. No. 4,221,574 discloses a process for making fiber by swelling a cellulose sheet using liquid-state tertiary amine oxide containing 5 to 15% by weight water as solvent at 65 to 95° C., followed by agitating and heating, and then, spinning.
This process, however, couldn't obtain homogeneous cellulose solution due to a film formed on the pulp sheet.
U.S. Pat. No. 4,416,698 discloses a process for making fiber by feeding solid-state NMMO(not liquid-state) and cellulose pulp into an extruder, followed by agitating them, and then, spinning. This process, however, is not suitable for a mass production because there remain a great amount of powder particles which are not dissolved in a solution by using two kinds of powder.
PCT WO 1997/47790 discloses a process for making fiber in which fibril type cellulose powder and high concentration NMMO aqueous solution containing 5 to 20% by weight water at 50 to 130° C. instead of a cellulose pulp sheet are fed into a twin-screw type extruder, followed by mixing and melting them, and then, spinning.
This process, however, has some disadvantages in that since during the spinning, there remains a great amount of power particles which are not dissolved and impurities in the resultant solution, and hence a filter for removing them must be very frequently replaced. It makes the cost of production too high because of changing filters too often. And a great amount of powder particles which are not dissolved in the solution couldn't obtain homogeneous cellulose solution, which makes physical and chemical properties of the obtained fiber deteriorated.
U.S. Pat. No. 4,416,698 and PCT WO 1997/47790 disclose a process for making cellulose solution through mixing, swelling (paste) and melting processes in an extruder. These processes, however, has a disadvantage in that they don't fully dissolve the cellulose.